A multimode radio in a related art is described in patent document 1. FIG. 14 shows a configuration example of the multimode radio in the related art compatible with radio system A and radio system B described in patent document 1.
In FIG. 14, an antenna 901 is shared between the radio system A and the radio system B. The antenna 901 is connected to a duplexer 902 of the radio system A and a duplexer 903 of the radio system B. In a transmission system, an in-phase baseband transmission signal is input from an in-phase baseband input terminal 916 to a low-pass filter 914. The in-phase baseband transmission signal is modulated by a quadrature modulator 913 and becomes an in-phase intermediate frequency transmission signal. A quadrature baseband transmission signal is input from a quadrature baseband input terminal 917 to a low-pass filter 915. The quadrature baseband transmission signal is modulated by the quadrature modulator 913 and becomes a quadrature intermediate frequency transmission signal. The in-phase intermediate frequency transmission signal and the quadrature intermediate frequency transmission signal are amplified by a variable gain amplifier 912 and unnecessary frequency components are removed through a low-pass filter 911. The in-phase intermediate frequency transmission signal and the quadrature intermediate frequency transmission signal are up converted by a transmission mixer 910 and are subjected to gain control by a variable gain amplifier 909 and becomes a transmission signal of the radio system A or the radio system B. When the multimode radio operates with the radio system A, a high frequency switch 908 connects to a power amplifier 906. When the multimode radio operates with the radio system B, the high frequency switch 908 connects to a power amplifier 907. The transmission signal of the radio system A is transmitted from the antenna 901 through an isolator 904 and the duplexer 902, and the transmission signal of the radio system B is transmitted from the antenna 901 through an isolator 905 and the duplexer 903.
In a reception system, when the multimode radio operates with the radio system A, a reception signal of the radio system A received at the antenna 901 is amplified by a low noise amplifier 919 through the duplexer 902. The amplified reception signal is subjected to frequency conversion by a reception mixer 921 and then passes through an intermediate frequency filter 923 corresponding to the reception frequency and becomes an intermediate frequency reception signal. The intermediate frequency reception signal is input to a variable gain amplifier 926 through an intermediate frequency switch 925. When the multimode radio operates with the radio system B, a reception signal of the radio system B received at the antenna 901 is amplified by a low noise amplifier 920 through the duplexer 903. The amplified reception signal is subjected to frequency conversion by a reception mixer 922 and then passes through an intermediate frequency filter 924 corresponding to the reception frequency and becomes an intermediate frequency reception signal. The intermediate frequency reception signal is input to the variable gain amplifier 926 through the intermediate frequency switch 925. The amplified intermediate frequency reception signal is demodulated by a quadrature demodulator 927 and becomes an in-phase baseband reception signal and a quadrature baseband reception signal. The in-phase baseband reception signal passes through a low-pass filter 928 and is output from an in-phase baseband output terminal 930. The quadrature baseband reception signal passes through a low-pass filter 929 and is output from a quadrature baseband output terminal 931.
A first local oscillator 918 outputs a transmission local oscillation signal corresponding to the radio system A and the radio system B to a transmission mixer 910. The first local oscillator 918 outputs a reception local oscillation signal corresponding to the radio system A and the radio system B to reception mixers 921 and 922. A second local oscillator 933 outputs a modulation local oscillation signal to the quadrature modulator 913 through a frequency dividing section 936. The second local oscillator 933 outputs a demodulation local oscillation signal to the quadrature demodulator 927.
The frequency dividing section 936 is made up of frequency dividers and switches setting the frequency dividing counts corresponding to the modulation local oscillation signal and the demodulation local oscillation signal of the radio system A and the modulation local oscillation signal and the demodulation local oscillation signal of the radio system B. A frequency divider 951 corresponds to the modulation local oscillation signal of the radio system A. A frequency divider 952 corresponds to the modulation local oscillation signal of the radio system B. The frequency divider 951 and the frequency divider 952 are switched by a switch 955. A frequency divider 953 corresponds to the demodulation local oscillation signal of the radio system A. A frequency divider 954 corresponds to the demodulation local oscillation signal of the radio system B. The frequency divider 953 and the frequency divider 954 are switched by a switch 956. At the radio system A operation time, the switch 955 connects to the frequency divider 951 and the switch 956 connects to the frequency divider 953. At the radio system B operation time, the switch 955 connects to the frequency divider 952 and the switch 956 connects to the frequency divider 954. The multimode radio includes as many frequency dividers as the number of covered radio systems and the number of modulation and demodulation combinations. As the frequency dividers are switched by the switch, the multimode radio in the related art can switch among radio systems using different frequency bands without increasing the number of local oscillators.
As an example of sharing and combining frequency dividers, a first frequency divider for dividing output of a local oscillator and a second frequency divider for dividing output of the first frequency divider are included. It is assumed that the output of the first frequency divider corresponds to a first radio system and the output of the second frequency divider corresponds to a second radio system. The frequency divider inputs an in-phase local oscillation signal and a quadrature local oscillation signal having a 90° phase difference to a quadrature modulator and a quadrature demodulator. To obtain output of the first frequency divider, the second frequency divider is connected to either of in-phase local oscillation signal output and quadrature local oscillation signal output of the first frequency divider. Here, it is assumed that the in-phase local oscillation signal output of the first frequency divider connects to the second frequency divider. When the multimode radio operates with the first radio system, the second frequency divider need not be operated and may be turned off by a switch. However, it is difficult to implement an open/short switch in IC in an actual circuit and the circuit operation is turned on/off by current control (non-patent document 1).
Patent document 1: JP-A-9-261106 (p. 4-p. 5, FIG. 2)
Non-patent document 1: “Analog IC no kinou kairo sekkei nyuumon” written by AOKI Hidehiko, CQ Shuppansha, p. 168